1. Field of the Invention
The invention relates to a radar system that is mounted on a vehicle or the like and detects an obstacle and/or a preceding vehicle ahead, and to a detection method.
2. Description of Related Art
A vehicle has already been available, on which a radar system is mounted to detect obstacles and/or preceding vehicles ahead of the vehicle and determine the relative distance to the obstacles and/or the preceding vehicles.
The radar system is mounted in a front portion of the vehicle and a transmitting antenna of the radar system outputs a transmitted wave ahead of the vehicle. When the transmitted wave hits the obstacles, the preceding vehicles, etc. and is reflected therefrom, the reflected wave is received by a receiving antenna of the radar system. The reflection source, such as the preceding vehicles and the obstacles, is herein collectively referred to as the target.
After the reflected wave is received by the receiving antenna, an arithmetic processing unit in the radar system calculates the relative distance between the vehicle and the target based on the time lag (delay time) between the transmitted wave and the reflected wave. In addition, the arithmetic processing unit is connected to the warning device and when, based on the result of calculation of the relative distance, it is determined that the target can approach the vehicle and collide with the vehicle, the arithmetic processing unit sends a warning command to the warning device. The warning device that has received the warning command sounds the alarm or displays a warning message to prompt the driver to decelerate the vehicle and/or avoid the obstacles and/or the preceding vehicles.
When the height of the target is low and the vehicle can easily run over the target, that is, when the target is an iron plate on the road, for example, the vehicle would not collide with the target and therefore, there is no need to send the warning command to the warning device. Thus, when a target is detected, the height of the target is determined and it is determined whether it is necessary to send a warning command.
As a method of determining the height of the target, a method that utilizes the intensity (amplitude) of the reflected wave has already been available. It is known that the intensity of the reflected wave varies depending on the relative distance between the vehicle and the target and that the trend of the variation depends on the height of the target. Japanese Patent Application Publication No. 2008-122391 (JP-A-2008-122391) describes that a curve of the intensity of the reflected wave in relation to the relative distance between a radar system and a target is obtained through experiments or the like, the curve is obtained for each height of the target, and the curves for the respective heights are stored in a memory of the radar system. The curve of the intensity of the reflected wave that is detected by the radar system while the vehicle is driven and the plurality of curves for the respective heights that are stored in the memory are compared with each other (subjected to the pattern matching), the curve that is minimum in the difference from the curve of the reflected wave that is detected by the radar system is extracted from among the curves for the respective heights stored in the memory, and the height of the target corresponding to the extracted curve is assumed to be the height of the target that is detected by the radar system.
In the conventional technology, the processing time to perform the pattern matching is required. Specifically, there has been a problem that a delay time corresponding to the processing time occurs before a warning command is sent to the warning device and the time that can be used to avoid the target is correspondingly shortened.